Steam turbines extract work from a flow of steam to generate power. A typical steam turbine may include a rotor associated with a number of wheels. The wheels may be spaced apart from each other along the length of the rotor and define a series of turbine stages. The turbine stages are designed to extract useful work from the steam traveling on a flow path from an entrance to an exit of the turbine in an efficient manner. As the steam travels along the flow path, the steam causes the wheels to drive the rotor. The steam gradually may expand and the temperature and pressure of the steam gradually may decrease. The steam then may be exhausted from the exit of the turbine for reuse or otherwise. Higher temperature steam turbines may generate increased output as the increased temperature of the steam increases the overall energy available for extraction.
Generally described, a typical steam turbine may include a high pressure section, an intermediate pressure section, and a low pressure section. The sections may be arranged in series with each section including any number of stages. Within the sections, work is extracted from the steam to drive the rotor. Between the sections, the steam may be reheated for performing work in the next section. The high pressure and the intermediate pressure sections may operate at relatively high temperatures so as to increase the overall steam turbine output.
Although higher temperature steam turbines may be capable of increased output, the higher temperatures may challenge the performance of the materials used to manufacture the turbine components. For example, at least some known combined cycle power plants include a steam turbine that is coupled to a gas turbine via a single shaft. Particularly when only the gas turbine is carrying a load, at least some of the steam turbine components may increase in temperature because of windage. As a result, higher temperature materials must be used for components such as the rotor. Such higher temperature materials tend to be relatively expensive and may be difficult to manufacture in the desired geometry.
There is therefore a desire for improved systems and methods of cooling steam turbine components, particularly about the wheel space and the rotor thereof. Such improved systems and methods of cooling may allow for the use of lower temperature materials and hence lower cost materials without sacrificing overall efficiency and performance.